This invention relates to a tape for use in tape-automated-bonding of integrated circuits, and to a method of producing such a tape.
Tape-automated-bonding is a known method of making connections to the interconnection pads of integrated circuits. A length of tape (such as conventional 35 mm film base) carries a series of interconnection arrays (also known as "frames") for integrated circuits. Each array comprises a number of etched copper "beams" (also known as "leads" or "fingers"), each beam being arranged for bonding with a respective interconnection pad of an integrated circuit. The bond between each beam and interconnection pad is made via a terminal (known as a "bump") which is formed either on the interconnection pad or at a corresponding location on the beam. Re-flow soldering or thermocompression is used to form the bond. Bumps formed initially on the interconnection pads of an integrated circuit are usually provided while the integrated circuit is still part of a larger wafer, and the provision of bumps is known as "wafer bumping".
Once bonded to the tape, individual integrated circuits and their respective interconnection arrays are excised from the tape for packaging--for example, connection to a "lead frame" of a conventional dual-in-line integrated circuit package, particularly a moulded plastics package. Alternatively, the tape-bonded integrated circuits may be directly connected to a hybrid substrate or printed circuit board.
The use of tape facilitates automation of the bonding process and automatic testing of bonded chips still on the tape (if the beams are electrically isolated). For such automatic testing, the tape is loaded on a reel-to-reel transport mechanism associated with an automatic testing machine.
Tapes are available for use in tape-automated-bonding of specified integrated circuits. These tapes have interconnection arrays which are appropriate for the specified integrated circuits, the etched copper beams of the arrays each being provided with, for example, a gold-plated copper bump. Such tapes are known as "bumped tapes". Some integrated circuits are also available having interconnection pads provided with gold-plated bumps for bonding to tape. Such integrated circuits are known as "bumped chips".
With known bumped tapes, however, the bumps can fail to provide consistently satisfactory bonds. We observed that a reason for this is that the bumps of, for example, copper formed on the copper beams have relatively hard, uneven bonding surfaces which, even after gold-plating, remain uneven and unyielding, causing poor adhesion to the aluminium, or other metal, interconnection pads of the integrated circuit.